1. Field of the Invention
This invention relates to an albada finder of which a view frame is formed on an object side surface of an eyepiece lens group, and a half mirror is formed on an eye point side surface of an objective lens group.
2. Description of the Prior Art
For example, the conventional albada finder is disclosed by Japanese Laid Open Publication No. Sho 57-624. The finder of the publication is composed of an objective lens group, which consists of two negative lenses, and an eyepiece lens group which consists of two positive lenses arranged in this order from the object side.
A view frame is formed on the object side surface of the eyepiece lens group, and a half mirror is formed on the eye point side surface of the objective lens group. An user can observe the image of the view frame reflected by the half mirror and the photographic subject image passed through the half mirror in an overlapping fashion.
In this specification, distance from the 1st surface of the finder system to the 8th surface (the last surface) is defined as lens full length, distance from the 8th surface to an eye point is defined as eye relief, and sum of the lens full length and eye relief is defined as finder full length.
Since the above-mentioned conventional albada finder has a short lens full length from the 1st surface to the 8th surface, it has the long eye relief in order that the finder full length coincides with thickness of a camera body. Although eye relief of the finder for cameras is about 15 mm in general, the eye relief of the finder of the above mentioned publication is 20 mm.
However, since the conventional albada finder has a short lens full length, the 4th lens, which is disposed in the most eye point side, is mounted inside a camera body at a position spaced from the back side of the camera body. For this reason, if the cover glass is not prepared, dust will enter the space formed behind the 4th lens of the finder, and it is difficult to remove the dust.
Moreover, since the conventional albada finder has a large distance between an eye and the eyepiece lens group, it must enlarge the diameter of an eyepiece lens group in order to obtain the proper visual angle.